Are wider tyres really faster?

In the past, narrow tyres were the order of the day, but the modern peloton is bucking the trend and switching to wider hoops. Tyre companies are unanimous in their support for this increase in diameter, which they claim reduces rolling resistance and saves energy, as well as adding extra comfort. No longer does thinner mean faster.

It’s not just the tyre brands making the change. Bike manufacturers are also taking heed of the trend and fitting their machines with 25mm tyres as standard — instead of the formerly ubiquitous 23mm size. As a result, tyre clearances are expanding. Frames that were once too narrow for anything other than skinny race tyres now have room for fatter fitments.

The root of this trend is found in the pro peloton. Nothing new there. On a long stage, it’s easy to see why comfort — increased with a wider tyre — factors so highly.

Getting a rider to the climax of a stage race in good shape helps them to deliver the knockout blow. If they’re spending the day feeling every road imperfection, fatigue is exacerbated — no matter how quickly they get to the business end, no matter how good their lead-out — their performance will be compromised.

Sizeable benefits

At the extreme end of the scale, look at Paris-Roubaix, in which most teams use 28mm or 30mm-wide tyres. When deciding on tyre pressure, the weather conditions must be considered, and it’s not always easy to hit the sweetspot of comfort, speed and handling. The number-one priority is getting the rider and their bike to the finish in one piece.

Paris-Roubaix may differ wildly to the riding the majority of us do, but our tyre choice shouldn’t be any less considered. The contact points between our bike and the road are what keep us shiny-side-up, after all.

A wider tyre has a larger contact area with the road beneath our wheels, adding a modicum of extra traction — a welcome attribute in wet conditions — and making pinch-flats less likely.

Then there’s rolling resistance.
The performance of a wider tyre is less compromised by lower pressures, compared to a 23mm tyre. But in a cycling world obsessed with aerodynamic advantages, surely wider is slower?

It’s easier to accommodate wider tyres on wider rims, thus avoiding detrimental effects on aerodynamics. On a narrow, 19mm rim, a bigger-profile tyre balloons, causing more drag, so that any advantage gained from the decreased rolling resistance is void by the increased drag. A wider, 23mm rim with a 25mm tyre allows the rim and tyre to sit flush with each other, thus making airflow far smoother.

Counting the costs

Practically, there is one downside. Switching tyres is relatively cheap, but if it necessitates buying new wheels to get the most out of the shift, it suddenly becomes a far less attractive prospect. Pounds in the till to save watts on the hill? It just depends how far you are willing to go.

Wider tyres: yes or no

Yes: Rob Scullion, Cambrian Tyres (UK distributors for Continental)

“25mm tyres have been proven in various tests to be more efficient than 23mm tyres. The 28mm GP4000S II is faster in the lab than the 23mm and 25mm version, but in the real world, aerodynamics come into play and hinder efficiency. With a smaller contact patch on the road, the 25mm is the perfect all-round package for speed, grip and comfort. It is the size all our race teams choose.”

No: Michael Hall, Zipp wheel development director

“The trend to move to a wider tyre comes with a slight advantage in rolling resistance over narrower tyres. A reasonable-performance improvement when going from a 23mm to a 25mm tyre would be a reduction in rolling resistance of 10 per cent or about three watts at 40kph. However, when evaluating the aero affects of such a change on Zipp Firecrest rims on a TT bike set-up, we found the opposite.”

If wider tyres work for the pros, then they can work for us too

Our take

How far can we go before we turn our carbon race bikes into glorified Boris bikes? The key is striking a harmonious balance between rolling resistance and aerodynamics. The other factors — the reduced risk of pinch-flats and being able to lower tyre pressures for comfort and better handling — are a done deal. If 25mm is good enough for the pros, it’s definitely good enough for us average Joes.

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